Treating a heartworm infestation is
difficult and dangerous. It is far easier and more effective to prevent the
problem in the first place. In theory, the best way to prevent heartworms is to
keep your dog from being bitten by a
mosquito. Unfortunately, preventing mosquito bites can never be 100 percent
effective. Dogs can be reasonably protected if they remain indoors in the late
afternoon and evening, when mosquitoes are feeding.
Areas of most frequent heartworm infestation are along coastal regions,
where swamps or other brackish water provide ideal conditions for mosquitoes to
breed. Since mosquitoes have a flight range of one quarter mile, spraying
around the yard and kennel and removing standing
water can be partially effective, but they will never eliminate the threat.
Inflammatory bowel disease (IBD) occurs when a dog’s stomach and/or intestine becomes home to an unusually high number of inflammatory cells. These cells cause changes in the lining of the digestive tract, which inhibit the normal absorption and passage of food.
It is important to note that although some of the symptoms may be similar, IBD is not the same as irritable bowel syndrome, which is caused by psychological stress rather than a physiological abnormality.
If you live or travel with your dog in an area where heartworm is endemic,
your dog should be on a heartworm prevention program. Ask your veterinarian
about local prevalence and follow their recommendations for prevention. Most
dogs should be on a heartworm preventive program.
A prevention program should be started at 6 to 8 weeks of age in endemic
areas, or as soon thereafter as climate conditions dictate. In the Deep South,
where mosquitoes are a year-round problem, dogs should be kept on preventive
drugs all year long. In areas where it is not necessary to administer the drug
year round, start one month before the mosquito season and continue one month
beyond the first frost (generally from May or June to November or December).
Heartworm prevention is important for the dog’s whole life. Some owners may
elect to give heartworm preventives year round for zoonotic parasite protection
and to reduce the risk of breakthrough heartworm disease in case they miss a
monthly dose. All dogs 7 months and older should have an antigen test for
heartworms before starting a prevention program. If the test is positive, a
microfilaria concentration test should be performed. The antigen test should be
repeated annually or as frequently as your veterinarian recommends-even if the
dog is on a heartworm prevention program. Many heartworm preventives can cause
illness if given to a dog with circulating microfilaria.
There are a number of drugs currently in use as heartworm preventives. They
include ivermectin (Ivomec, Heartgard),
milbemycin oxime (Interceptor), and selamectin (Revolution).
Heartgard is an effective preventive that is given once a month. This drug
acts on the L4 larvae. It has the advantage that dogs do not have to
be heartworm-free to initiate therapy; dogs infected for as long as two months
before treatment will not develop heartworms. If a monthly dose is missed,
restart the drug and obtain a heartworm antigen test seven months later.
Heartgard is marketed in chewable tablets of different sizes, depending on the
weight of the dog. The recommended dose is generally considered to be safe to
use on Collies and other herding breeds. However, with safer alternatives
available, most owners avoid this for the breeds with the genetic defect that
causes sensitivity to ivermectin.